Conventionally, some techniques to prevent fogging of a lens have been proposed. Fogging prevention is divided in terms of actions into two broad types: using a so-called wetting phenomenon; and coating a lens surface with water-absorbing resin. Here, the former type of using a wetting phenomenon is to narrow a contact angle with respect to water attached to a lens so as to prevent the water from becoming droplets, and application of surfactant on a lens surface is the most common way. However, in a case where surfactant is applied, it is difficult to maintain the antifogging performance. For example, the surfactant may come off easily from a lens surface when being wiped with water. Accordingly, a product having an enhanced fixing property with respect to a lens surface has been proposed, though antifogging performance thereof is still not maintained sufficiently.
Accordingly, attention is now focused on the latter type of coating (forming a water-absorbing layer) a lens surface with water-absorbing resin.
In a case of antifog coating using a water-absorbing layer, it is common to knead surfactant into the water-absorbing layer and use both of water absorption and a wetting phenomenon in order to maintain an antifog property even when exceeding water-absorbing capacity. However, when the surfactant is lost by being washed with water or the like, a contact angle with respect to a water-absorbing layer surface is widened (50 to 90 degrees) and therefore visibility is extremely lowered by scattering of light by water droplets due to condensation by exceeding the water-absorbing capacity.
Moreover, a water-absorbing layer has problems due to the nature thereof, such as low slippage of a surface, especially low strength at the time of water absorption or low weather resistance or the like.
Examples of such an antifog coating technique having improved slippage and strength of a water-absorbing layer are Patent Document 1, Patent Document 2 and Patent Document 3. In these antifog coating techniques, a water-absorbing layer is first formed and then a water-repellent layer is formed on the surface of the water-absorbing layer, so as to improve slippage and strength.